The present invention relates to a method for determination of positions of objects.
In order to determine the distance between fixed or mobile measuring locations and fixed or mobile measurement objects, a number of different methods are known which are adapted to different types of measurement equipment. Certain methods may be described as active in the sense that the measurement equipment illuminates the measurement object, for example by means of laser light or radio frequency signals such as radar pulses. Other methods may be said to be passive due to the fact that the measuring object's own radiation is utilized during the measurement. In these cases, the range determination is carried out almost exclusively indirectly by means of angular measurements. The properties of the measurement object within the range of visible light are thus used for determining the direction to the measurement object by means of optical methods, the heat radiation of the measurement object by means of measurements with infrared-sensitive equipment or, if the measurement object itself emits sound or radio frequency radiation, by means of receiver equipment for these frequencies, for example a sonar or a "listening" radar, respectively.
The passive methods for determining the range (and thus also the position) of a measurement object have the property of not distorting the measurement object, which is an advantage in many applications, but on the other hand the position of the measurement object can not be determined by means of measurements from a single measuring location. If the measurement object is mobile, a time factor is also added--measurements from different measuring locations must be coordinated in time.
Different passive methods for range determination by means of angular measurements are known. One method which nowadays is called TMA (Target Motion Analysis) is known from the Second World War, during which it was utilized by submarines for determining the range and course of the target. The method is based on the fact that by means of passive sonar equipment, the direction to the target is determined while the submarine moves in a certain fashion. Thus, a course is firstly followed which leads away from the target direction and thereafter back towards the original target direction. During these two legs, repeated measurements of the direction to the target are made. By assuming that the speed and course of the target are constant, the location and movement of the target may be calculated by means of the angular measurements and known algorithms.
The difficulties with the method are primarily to decide how long the legs should be and to decide in which direction it is most advantageous to steer. Long legs (a large measurements base) are required in order to obtain a high accuracy of the measurements when the distance to the target object is long. If the distance is short, there is however no time or need for long legs. The problem is that there is no basis for decisions regarding the length of the legs until, at the earliest, the beginning of the second leg. The problem is particularly serious if the first leg happens to be chosen in the direction which gives a small or, in the worst case, no change of the direction to the measurement object.
The object of the present invention is thus to provide a measuring method by means of which it is possible to determine the position of a measurement object in a quicker way by means of angular measurements, and with a higher measuring accuracy than in previously known methods.